Discrete element light modulating microstructure devices

ABSTRACT

A light modulating or switching array ( 10 ) having a plurality of discrete protrusions ( 16 ) formed of electro-optic material, each of which is electrically and optically isolated from each other. The protrusions ( 16 ) have defined a top face ( 20 ), a bottom face ( 30 ), first and second side faces ( 22, 24 ), and front and back faces ( 26,28 ). There are a plurality of electrodes ( 34 ) associated with each of the protrusions ( 16 ), these electrodes ( 34 ) being capable of inducing an electric field in the electro-optic material for independently modulating a plurality of light beams which are incident upon one of the faces ( 20, 22, 24, 26, 28, 30 ) of the protrusions ( 16 ). The electro-optic material may be of PLZT, or a member of any of the groups of electro-optic crystals, polycrystalline electro-optic ceramics, electro-optic semiconductors, electro-optic glasses and electro-optically active polymers. Also disclosed is a light modulating array ( 10 ) of the type having a matrix ( 136 ) of electro-optic material which contains a plurality of embedded adjacent electrodes ( 134 ). These electrodes ( 134 ) are capable of inducing an electric field in the electro-optic material for independently modulating a plurality of light beams which are incident upon the matrix ( 136 ) of electro-optic material. This matrix ( 136 ) can be formed by a variety of processes, including a sol-gel process. Additionally disclosed is a system ( 11 ) in which light modulating arrays ( 10 ) are used to modulate incident light beams ( 42 ) and separate them into a plurality of data channels ( 94, 96 ).

TECHNICAL FIELD

[0001] The present invention relates generally to light modulators andlight switches, and more particularly to electro-optic modulator arrays.The inventor anticipates that primary application of the presentinvention will be in high-speed printing and image processing, althoughit may also be used in optical interconnects, telecommunications andflat panel displays.

BACKGROUND ART

[0002] Electro-optic modulators have been well known in the art foryears, but for multi-channel applications they have suffered fromseveral disadvantages. Prior art modulator arrays have usually beenformed from single wafers of electro-optically active material ontowhich surface electrodes have been attached, to form channels which aredefined by the electric field lines within the optical wafer.Cross-talk, or interference between channels, has been a problem becauseelectro-optic modulators are vulnerable on at least two levels. Sincethe channels are not restricted except by the electric field lines,activity in one channel can easily induce electro-optic interference ina nearby channel. This is in addition to usual electrical cross-talkexperienced by closely grouped and unshielded electrical contacts. Also,previous electro-optic modulators and light switches have often reliedon surface deposited electrodes, which produce electric field lines thatare fringed, rather than channeled and directed. Due to the exponentialdecay of the electric field intensity inside the material, very highvoltages may be required to drive the material to produce the desiredelectro-optic effect.

[0003] Electro-optic materials, such as LiNbO₃, can be expensive, andcan require high driving voltages. Liquid crystal modulators have alsobeen used, but response times for this type are typically very slow, onthe order of milliseconds. Also, the electro-optic effect exhibited by amaterial can be of several different orders, depending on the material.A first order effect, called the Pockels effect, is linear in itsresponse to increase in applied voltage. A second order effect, calledthe Kerr effect, is quadratic in its response, thus a greater increasein effect can be produced relative to an increase in voltage. This cantheoretically allow smaller driving voltages in a primarily Kerr effectmaterial to be applied to produce a comparable electro-optic effectcompared to material which produces primarily Pockels effect.

[0004] Lead zirconate titanate polycrystalline ceramic which is dopedwith lanthanum (PLZT) is a relatively inexpensive, optically transparentceramic which can be made to exhibit either the quadratic Kerr effect orthe linear Pockels effect, depending on the composition, and can beformed into wafers easily and used in sol-gel moldings. The concentrateof lanthanum, or “doping”, is variable, and can lead to varyingcharacteristics in the material. PLZT that is commercially available istypically made from a “recipe” which produces a very high dielectricconstant κ. Very high κ values produce high capacitance values C, whichin turn produce high power requirements, as power (P) is proportional toCV²/2 where V=voltage. High power consumption in turn generates heat, sothat some modulators that require high voltage also may require cooling.If the proportion of lanthanum dopant, or other components, in thematerial is adjusted, the dielectric constant value and electro-opticconstant value, as well as the type of electro-optic effect (Kerr orPockels), may also be varied, with the result affecting capacitance andpower consumption.

[0005] Prior art inventions for modulating light in arrays generallysuffer from common problems experienced by multi-channel optical andelectrical systems in which the channels are not appropriately isolated.As discussed above, interference is easily induced in nearby channelsresulting in cross-talk which can distort image clarity and corrupt datatransmissions. Additionally, much of the prior art requires high drivingvoltages that are incompatible with TTL level power supplies.

[0006] U.S. Pat. No. 4,746,942 by Moulin shows a wafer of PLZTelectro-optic ceramic material with a large number of surface mountedelectrodes. This invention suffers from the disadvantage of cross-talkbetween channels, although there is discussion of attempts to decreasecross-talk by use of large electrodes and increased space of theelectro-optic windows. This results in less efficient use of thematerial. Although typical driving voltages are not given, with largerareas of material, higher applied voltages become necessary to providethe necessary electric field density in the wafer.

[0007] U.S. Pat. No. 4,867,543 by Bennion et al. describes a spatiallight modulator made of a solid sheet layer of electro-optic materialsuch as PLZT, which has paired surface electrodes. This has thedisadvantage of requiring a driving voltage of approximately 20 volts toproduce a phase retardation of PI radians. U.S. Pat. No. 4,406,521 byMir et al. discloses a panel of electro-optic material which useselectrodes to define pixel regions. It speaks of using voltages in therange of 100-200 volts. U.S. Pat. No. 5,033,814 by Brown et al. alsoshows a single slab of electro-optic material which requires a drivingvoltage of 150 volts. U.S. Pat. No. 5,528,414 to Oakley discloses asingle wafer of Pockels crystal with surface mounted electrodesrequiring a 70 volt driving voltage. Besides being obviouslyincompatible with TTL voltage levels, none of these inventions have anymechanism for confining electric field lines. Also, in general, use ofhigher driving voltages will generate heat in the electro-opticmaterial, which can mean that a cooling system may be required.

[0008] U.S. Pat. No. 5,220,643 by Collings discusses an array of opticalmodulators which are built into a neural network. These modulators aremostly of liquid crystal type, although use of PLZT is mentioned. U.S.Pat. No. 4,560,994 by Sprague shows a single slab of electro-opticmaterial with an array of electrodes which create fringe electricfields, which are not channeled. Sarraf's U.S. Pat. No. 5,521,748 alsodiscloses a modulator array in which mirror-like devices deflect ordeform when electrostatic force is applied. U.S. Pat. No. 4,367,946 toVarner also discusses a light valve array, with one specificallypreferred material being PLZT. However, all four of these inventions canbe expected to have the same problems of cross-talk, which the presentinvention is designed to eliminate.

[0009] For the foregoing reasons, there is a need for an array ofdiscrete light modulating elements which can operate at TTL voltagelevels, and at high speeds, with almost no cross-talk, and which can beused to produce small pixels or which can be grouped together to createlarger pixels and large two dimensional panels or sheets.

DISCLOSURE OF THE INVENTION

[0010] Accordingly, it is an object of the present invention to providean array of discrete modulated elements of electro-optic material.

[0011] Another object of the invention is to provide arrays ofelectro-optically modulators that can be driven by TTL voltages, andthus be compatible with standard TTL power supplies.

[0012] Yet another object of the invention is to produce arrays ofelectro-optic modulators which have very little cross-talk betweenchannels.

[0013] Still another object of the present invention is to provide anarray with very fast response and switching time.

[0014] A further object of the present invention is to provide an arrayof pixels which can be of very small dimensions to reduce problems ofaliasing in optical displays.

[0015] A yet further object of the present invention is to produce lightmodulating arrays that can be manufactured by conventional methods veryinexpensively.

[0016] Briefly, one preferred embodiment of the present invention is alight modulating array having a number of discrete protrusions formed ofelectro-optic material, each of which is electrically and opticallyisolated from each other. The protrusions each can be viewed as having atop face, a bottom face, first and second side faces, and front and backfaces. Each array also has a number of electrodes associated with eachof the protrusions, the electrodes being capable of inducing an electricfield in the electro-optic material for independently modulating anumber of light beams which are incident upon one of the faces of theprotrusions. The protrusions can be made from any number ofelectro-optic materials including electro-optic crystals,polycrystalline electro-optic ceramics, electro-optically activepolymers, electro-optic semiconductors and electro-optic glasses. Theprotrusions can be integral with a substrate wafer, or formed upon asubstrate of a second material. The electrodes can be attached in avariety of positions including on the sides, top and bottom, and on thefront and back faces if electrodes with apertures are used.

[0017] A second preferred embodiment of the present invention is a lightmodulating array having a number of discrete protrusions formed ofelectro-optic material, each of which is electrically and opticallyisolated from each other, each protrusion being formed in a prism shape.Each protrusion has a top face, a bottom face, and front and rear faces.Each array also has a number of electrodes associated with each of theprotrusions, the electrodes being capable of inducing an electric fieldin the electro-optic material for independently modulating a pluralityof incident light beams. Each of the prism shaped protrusions isoriented with respect to a number of light beams such that each lightbeam incident upon the front face of each protrusion enters theprotrusion traveling a first path and emerging at a first angle from therear face of the protrusion when no voltage is applied toelectro-optically activate the protrusion. However, each light beamtravels a second path and emerges at a second angle from the rear faceof the protrusion when the protrusion is electro-optically activated byapplication of appropriate voltage.

[0018] A third preferred embodiment of the present invention is a lightmodulating array having a matrix of electro-optic material, with eachmatrix containing a number of embedded adjacent electrodes. Theelectrodes are each capable of inducing an electric field in theelectro-optic material for independently modulating a number of lightbeams which are incident upon the matrix of electro-optic material.

[0019] A fourth preferred embodiment of the present invention is asystem for modulating light having a number of discrete protrusionsformed of electro-optic material and a number of electrodes, as above.The system also includes a power supply capable of supplying sufficientvoltage to induce a desired polarization shift from a first polarizationorientation to a second polarization orientation in a beam of polarizedlight entering the protrusions. Also included are a switches forcontrolling application of voltage to the electrodes through a conductorand a separator for separating light of a first polarization orientationfrom light of a second polarization orientation. The separator could beany of a number of mechanisms, such as beam splitters, cross-polarizers,etc.

[0020] An advantage of the present invention is that it may be operatedwith TTL voltages or lower.

[0021] Another advantage of the invention is that because of the lowvoltage requirements, heating of the elements is reduced andrequirements for cooling are minimized.

[0022] Yet another advantage of the present invention is that very smallelements may be produced, thus allowing for very fine image resolution.

[0023] A further advantage of the present invention is that cross-talkbetween channels is nearly eliminated.

[0024] A still further advantage of the present invention is thatstandard micromachining operations can be used, allowing for inexpensivemanufacture.

[0025] A yet further advantage of the present invention is that sol-gelprocesses can be used to create arrays very inexpensively.

[0026] Yet another advantage of the present invention is that sol-gelprocesses can be used to make displays which are both thin and flexible.These molding processes can produce arrays with large numbers ofelements quickly and for very low cost.

[0027] These and other objects and advantages of the present inventionwill become clear to those skilled in the art in view of the descriptionof the best presently known mode of carrying out the invention and theindustrial applicability of the preferred embodiment as described hereinand as illustrated in the several figures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The purposes and advantages of the present invention will beapparent from the following detailed description in conjunction with theappended drawings in which:

[0029]FIG. 1 is a perspective view of a system for modulating andswitching light beams which uses a light modulating array, showing themodulation of impinging light beams;

[0030]FIG. 2 is a perspective view of a modulator array, and electricalcircuit showing an alternative location for conductive pads;

[0031]FIG. 3 is a perspective view of a modulator array, and electricalcircuit showing the elements mounted on a substrate of differentmaterial;

[0032]FIG. 4 is a perspective view of a modulator array and electricalcircuit in which electrodes have been attached to the top and bottomwafer surfaces;

[0033]FIG. 5 is a perspective view of a modulator array and electricalcircuit showing an alternate location for conductive pads;

[0034]FIG. 6 is a perspective view of an alternate embodiment of amodulator array and electrodes;

[0035]FIG. 7 is a perspective view of another alternative embodiment ofa modulator array and electrodes;

[0036]FIG. 8 is a perspective view of system for modulating andswitching light beams which uses a modulator array and beamsplitters toseparate modulated and unmodulated beams into different channels;

[0037]FIG. 9 is a plan view of a system for modulating and switchinglight beams, which shows a single element of a modulator array used asan alternate mechanism for separating modulated and unmodulated beamsinto different channels;

[0038]FIG. 10 is a perspective view of a system for modulating andswitching light beams which shows a single element of a differentversion of a modulator array used as an alternate mechanism forseparating modulated and unmodulated beams into different channels;

[0039]FIG. 11 is a perspective view of a modulator array in whichelectrodes have been placed so as to produce an electric field which iscollinear with the direction of light propagation; and

[0040]FIG. 12 is a cross-sectional view of an embedded electrode arrayin a sol-gel matrix of electro-optic material.

BEST MODE FOR CARRYING OUT THE INVENTION

[0041] A preferred embodiment of the present invention is an array oflight modulating and switching microstructure devices. The presentinvention solves many of the problems of the prior art by usinglanthanum doped lead zirconate titanate crystal (PLZT), which is anoptically transparent ceramic that becomes birefringent when propervoltage is applied. PLZT has a quadratic electro-optic response tovoltage increase thus allowing lower driving voltages. In addition, thepresent invention uses an optimized compositional “recipe” in which theproportion of lanthanum dopant and matrix elements has been designed toproduce low dielectric constant κ, higher electro-optic efficiency, andthus low power requirements. Additionally, the electro-optic elementsare 3-dimensional and of very small size, generally 10 μm-200 μm in thelight propagation direction, or much less, depending on the design. Thisallows production of very high-density electric fields in these elementsby using small voltages, including TTL levels of approximately 5 volts,and lower. This has advantages because power supplies that are alreadyset up for TTL level digital components can supply the electro-opticmodulators as well. Cross-talk has been nearly eliminated by the use ofgrooves or regions which are filled with air or other dielectricmaterials. These physically separate at least a portion of the elements,thus directing and channeling electric field lines more closely. PLZT,as well as other electro-optic materials, also allows for pico-secondresponse time, thus theoretically allowing very high switchingfrequencies of 100 GHz and more.

[0042] The use of embedded electrodes produces more uniform electricfield strength in the elements. This allows a much lower driving voltageand a much more predictable and controllable electric field.

[0043] The present invention is also useful when using standard recipeelectro-optic materials, in which the dielectric constant has not beenminimized, and also in a variety of other electro-optic materials besidePLZT. Electro-optic materials fall generally into five categories, 1)electro-optic crystals, 2) polycrystalline electro-optic ceramics, 3)electro-optically active polymers, 4) electro-optic semiconductors, and5) electro-optic glasses. Although the electro-optic properties of thematerials are variable depending on composition, the present inventioncan be implemented with materials of any of these three categories.Specific examples of electro-optic materials besides PLZT which may beused include, but are not limited to, LiNbO₃, LiTaO₃, BSN, PBN, KTN,KDP, KD*P, KTP, BaTiO₃, Ba₂NaNb₅O₁₅, GaAs, InP, CdS, AgGaS₂, and ZnGeP₂.The very small dimensions of the elements result in very low elementcapacitance even when using material having a relatively largedielectric constant κ.

[0044] As illustrated in the various drawings herein, and particularlyin the view of FIG. 1, a form of this preferred embodiment of theinventive device is depicted by the general reference character 10.

[0045]FIG. 1 illustrates an array of light modulating microstructures 10as well as a system 11 for modulating or switching light in a number ofindependent channels. In this preferred embodiment, the array 10 isformed from a wafer 12 of PLZT. PLZT has been chosen for its largeelectro-optic effect and low absorption for thin wafers.

[0046] If PLZT is used, the relative proportion of the Lanthanum dopantin the ceramic can be very important in determining the driving voltagerequired for the elements. The composition also is important inestablishing the optical properties such as transparency, grain size andpore size, speed, power dissipation, operating temperature and formaximizing both the linear and the quadratic electro-optic coefficientsof the material. Commercial recipes for PLZT have largely used Lanthanumconcentrations of 9.0% to 12%. If Lanthanum concentration is varied inthe range of 8.5% to 9.0% of the PLZT ceramic and the concentration ofZirconium and Titanium are unchanged from typical ratios of 65/35, itmay be possible to achieve a higher quadratic electro-optic coefficient(R) in the PLZT for the La dopant percentage closer to 8.5%. For thePLZT compositions, where Zr and Ti are maintained in a 65/35 ratio andthe overall percentage of La is varied:

La=9.5%, R=1.5×10⁻¹⁶ m ² /V ²;

La=9.0%, R=3.8×10⁻¹⁶ m ² /V ².

[0047] It is known that for La<8.0%, PLZT loses quadratic electro-opticproperties. It is therefore expected that somewhere around 8.5% La thereshould be a maximum for R around (5-40)×10⁻¹⁶ m²/V².

[0048] This enhanced value of electro-optic coefficient provides manyadvantages. It will permit lower required driving voltages, and thuslower power dissipation in the material and hence lower heating of thedevice. This in turn allows the device to be driven at significantlyhigher frequencies, even without external cooling. Also, the use oflower La concentrations (which is a free electron donor) will result ina reduced “charge screening” effect. The overall result is highermodulation efficiency of devices manufactured from this material.

[0049] The wafer 12 has regions or grooves 14 formed to produceprotrusions 16 from the original thickness 18 of the wafer 12. Thegrooves 14 may be formed by any number of means, such as mechanicalmachining with micro-saws, chemical etching using photo-resist masks, orlaser ablation, or the array may be molded in shape from polycrystallineceramic, among other methods. The grooves 14 provide isolation betweenthe channels of the array 10, serve to direct and channel the electricfield lines in the electro-optic material and thus allow the array tooperate with nearly zero cross-talk.

[0050] Each protrusion 16 has a top face 20, a first side face 22 and asecond side face 24, a front face 26 and a rear face 28. The grooves 14can be cut through the entire original thickness 18 of the wafer 12, inwhich case, the protrusions will have an independent bottom face 30, orif the groove is not cut through the entire original thickness 18, thebottom face 30 will be integral with the wafer 12, as shown by thedotted line in FIG. 1.

[0051] The faces of the wafer 32 can be polished either before or afterthe grooves 14 are formed, to prevent scattering of light entering orleaving the wafer 12. Electrodes 34 are attached to the protrusions 16by any of a number of ways, but one preferred method is to embed theelectrodes 34, as this may produce a more uniform electrical field. Itis also possible that the material of the electrode 34 may completelyfill the grooves 14. Conductive pads 36 of gold or some other metal orconductive material are used to attach electrical leads 38 to theelectrodes 34, which connect them in turn to the electrical power supply40. An electrical field is thus established which is oriented in atransverse direction relative to the direction of the incoming lightbeams 42. The width of electro-optic material between the grooves 14 inthe protrusions 16 establishs the electrode gap 44 in this configurationof electrode 34 placement.

[0052] For ease of reference, an assembly containing a protrusion 16,attached electrodes 34, and conductive pads 36 shall be referred to asan “element”. The size of the wafer 12, the protrusions 16 and theelectrode gaps 44 will depend on the material chosen, and the desiredrange of applied voltages to be used. The electro-optic effect exhibitedby an element of a particular material depends on the electric fieldstrength within that element. The density of that field will in turndepend on the amount of applied voltage, the material chosen, and thephysical dimensions of the element in which the electric field iscontained. Using very small elements allows a large concentration ofelectric field density by use of small to moderate voltages. In thepresent invention, in order to use voltages in the TTL range, around 5V,it is estimated that the physical size of the elements, if made of PLZT,will be on the order of 20 μm×20 μm×200 μm. The grooves 14 can be madevery small, and indeed may be limited by the size of machining toolsused to form them. Excellent results in terms of near zero cross-talkhave been achieved using micro-sawing methods where the kerf size of thesaw cuts are around 25 μm. Effective reduction of cross-talk betweenchannels may be achieved with grooves as small as 5 μm.

[0053] Such tiny elements can produce modulated beams of very smallsize, producing such fine image resolution that the unaided eye isincapable of distinguishing it. It may have applications wheremicroscopic images are required, or where multiple beams are combined ingroups of 5 or 10 elements to make up 1 pixel in a display device.

[0054] The size of the elements will also depend on whether the beam istransmitted through the element or reflected from a rear surface, inwhich case, the length or the driving voltage can be cut roughly in halfto produce the same degree of modulation. Materials with smallerelectro-optic properties may require greater size or increased appliedvoltage to achieve proper modulation results.

[0055] In FIG. 1, a first element 46 and a second element 48 are shown,which in this preferred embodiment, will be assumed to be composed ofPLZT. Between the first element 46 and the voltage supply line, an openswitch 50 is shown to represent that the element 46 has no voltageapplied, and is in an inactive state. It is, of course, to be understoodthat nothing so primitive as throw-switches need be used to practice theinvention. Most likely, very high frequency (perhaps as much as 100 GHzor more) square waves of appropriate voltage will be used, butthrow-switches are used here as an easy means of illustrating the stateof the applied voltage.

[0056] The incoming light beams 42 having incoming linear polarization54 which is aligned with the upper tip 45 degrees to the left ofvertical, (which shall be referred to as “R” polarization) impinge onboth elements 46 and 48. This incoming light may be linearly polarizedlaser light, or it may be initially unpolarized light, perhaps evenincluding light from an incandescent bulb, which has been transmittedthrough a polarizer to produce linearly polarized light. First element46 is inactive, thus the outgoing polarization 56 of the first element46 is unchanged. It passes through an R aligned polarizer 60 and isdetected by a light sensor or photo detector 62, perhaps to berecognized as a digital “1”.

[0057] In contrast, switch 52 is closed leading to the second element48, thus the supply voltage is applied and the element 48 is active. Theelement 48 becomes birefringent under the influence of the appliedelectric field. Birefringence causes an incoming beam 42 which islinearly polarized at a 45 degree angle relative to the direction of theapplied electric field to split into two orthogonal components which arerespectively parallel and perpendicular to the electric field lines.These components travel along the same path but at different velocities.The electro-optic effect thus will cause a phase shift between the twocomponents, as one is retarded in relation to the other. After travelingthrough the element 48, the components re-combine with the result thatthe polarization of the emergent beam 58 is changed. If the voltage issufficient to cause a λ/2 shift in polarization, the polarization willbe rotated by 90 degrees, relative to its original orientation. In FIG.1, it is assumed that a λ/2 voltage of 5 volts has been applied whichproduces a 90 degree phase shift to give a linearly polarized outputbeam 58, which is oriented with the upper tip now 45 degrees to theright of vertical (which shall be referred to as “S” polarization). ThisS polarized light is now blocked by the R aligned polarizer 60, whichallows no light to reach the detector 62. This may be recognized by adigital device as a “0”.

[0058] If the applied voltage causes a λ/4 rotation, the outgoingpolarization 58 will be made into circular polarization, as the tip ofthe resultant electric field vector will describe a circle as itpropagates. Intermediate voltage values will result in ellipticalpolarization. These will be incompletely blocked by the polarizer 60,which will allow only the R aligned component to pass. Thus, the lightseen by the detector 62 may be theoretically controlled anywhere in therange from undiminished incoming intensity to total extinction, toproduce analog-type output signals if the appropriate control voltage isapplied.

[0059]FIG. 2 illustrates a different version of the modulator array 10.A wafer 12 is shown with attached or embedded electrodes 34, and in thisembodiment, the conductive pads 36 are located in a differentconfiguration for attachment to electrical leads 38.

[0060]FIG. 3 illustrates another version of the modulator array 10, inwhich the grooves 14 have been extended completely through the originalthickness 18 of the wafer. The elements 64 here are composed of theprotrusion 16 portions of the wafer 12 and their respective attached orembedded electrodes 22 and conductive pads 24 (see FIG. 1). A number ofelements 64 have been formed on a substrate 66 made from a differentmaterial which the bottom faces 30 now contact. This substrate 66 ispreferably a low dielectric material that is not electro-opticallyactive, such as SiO₂, for one example among many. The protrusions 16 maybe attached or glued to the substrate 66 prior to machining orattachment of the electrodes 34 and pads 36, or the completed elements64 may be assembled prior to attachment to the substrate 66.

[0061]FIG. 4 shows yet another version of the modulator array 10. Inthis embodiment, electrodes 34 are attached to the top faces 20 of theprotrusions 16 and a single large electrode 68 is positioned on thebottom side 70 of the wafer 12. It is to be understood that a pluralityof appropriately placed individual electrodes could be used on thebottom side 70 of the wafer 12 in place of the single large electrode 68pictured here and in the following FIG. 5. Conducting pads 36 areattached to the top and bottom electrodes 34, 68 as attachment pointsfor the electrical leads 38. Polished front faces 26 are indicated asbefore, and incoming light beams 42 are shown to indicate orientation.The polarization direction has not been shown, as the principles ofphase retardation operate much the same as in FIG. 1, with a λ/2 shiftproducing a 90 degree rotation, etc. This placement of electrodes 34, 68produces a different orientation of transverse electrical fields, butstill retains the advantage of channel separation and minimization ofcross-talk which was unavailable in the prior art.

[0062]FIG. 5 shows a variation of the configuration in FIG. 4, in whichthe upper conductive pads 36 are located in a different orientationrelative to the wafer 12. The top and bottom electrodes 34, 68 arepositioned as in FIG. 4, to produce a transverse electric field. Thepolished front faces 26 and incoming light beams 42 are again shown fororientation purposes.

[0063] Although not pictured here, it is to be understood that thisarrangement of top and bottom electrodes and the variations inconductive pad locations seen in FIGS. 4 and 5 can be used with elementswhich have been positioned on a different substrate material, in themanner suggested by FIG. 3, if the substrate material has the properconductive properties. It may also be possible for elements to bedirectly attached to a single large bottom electrode which can act as asubstrate to support and position the elements. Alternately, theelectrodes may be attached or embedded on both sides of theelectro-optic material directly before mounting the assembled elementsonto a substrate.

[0064]FIG. 6 shows another version of an array 10 of modifiedprotrusions 72 which have either been formed on the original wafer 12 orformed separately on a substrate of different optically transparentmaterial 66 in a similar manner to the embodiment shown in FIG. 3. Themodified protrusions 72 are shown to be oriented with their long sidesparallel to the long edge of the wafer 12 or substrate 66, but it shouldbe understood that they may also be oriented with the long sides of theprotrusions 72 transverse to the long edge of the wafer 12 or substrate66. An incoming polarized light beam 42 enters from the bottom side 70of the wafer 12 or substrate 66 and is internally reflected on theangled first side face 74 and angled second side face 76 to reemergefrom the bottom side 70 of the wafer 12. If appropriate voltage has beenapplied to the electrodes 78, the resulting polarization of the emergentlight beam 80 will be modulated in the manner described above. Theangles of the faces here are chosen to allow total internal reflection,but it is to be understood that if a reflective coating is applied tothe faces, a variety of other angles may be used as well.

[0065]FIG. 7 illustrates yet another version of a modulator array 10 inwhich the protrusions 82 have been modified in another manner such thatthe angled second side face 84 of each has been angled to direct theemergent beam 86 out of the top face 20 of each protrusion 82. As inFIG. 6, the protrusions may be oriented in a transverse direction, adifferent substrate material may be used, and a reflective coating maybe applied to reflecting faces.

[0066]FIG. 8 shows a system 11 for modulating or switching light beamswhich uses the modulator array 10 in much the same configuration as inFIG. 1. An incoming linearly polarized beam 42 of polarization “R”enters a first element 46 which is inactive due to an open switch 50, sothat its exiting polarization 56 is unchanged. This enters abeamsplitter 88 that has been positioned so that light of R polarizationwill be reflected out of the beamsplitter at angle φ, as shown byreflected beam 90. In a second element 48, which is active, the voltageis assumed to be such as to produce a λ/2 shift, the polarization isrotated 90 degrees to “S” orientation, and this passes through thebeamsplitter 88, as shown by unreflected beam 92. These beams can beused to carry separate digital information, and may be designated“channel 1” 94 and “channel 2” 96. It is to be understood thatbeamsplitters can be used as a channel separation device with any of thevarious embodiments illustrated herein.

[0067]FIG. 9 shows a top plan view of another system 11 for modulatingor switching light beams which uses a different version of a lightmodulating array 10. A single protrusion 16 is shown, which is composedof a first block 98 or portion of material having an index of refractionN₁, and a second block 100 of material having index of refraction N₂. Aboundary 102 is formed at the junction of the two materials. One of thetwo blocks, in this case the first block 98, has top and bottomelectrodes 104. First block 98 is composed of electro-optic materialsuch that when electrodes 104 are uncharged, the electro-optic materialis inactive, and N_(1=N) ₂. When voltage is applied to electrodes 104,the first block 98 becomes active and the index of refraction changesfor polarization components which are aligned with the electric fieldlines so that for this polarization, N₁>N₂. When first block 98 isinactive, an incoming beam 106 is projected into the first block 98 atentry angle ε to a normal such that the beam passes through the boundarybetween the two blocks 98, 100 and emerges as unreflected light ray 108.When first block 98 is active the index of refraction is increased suchthat total internal reflectance (TIR) occurs, and the beam is reflectedback into the first block 98 at the boundary 102, and emerges asreflected light ray 110. The two emergent beams 108 and 110 areseparated by angle δ, which has been greatly exaggerated here. Theseseparated beams 108, 110, can be detected by sensors 112, and thus beused to establish channel separation for data transmission.

[0068] Alternatively, the protrusion 16 can be made from a singleintegral block of material, which has been electro-optically dividedinto portions or sections. A first section 98 may have electrodes 104attached to induce a different index of refraction in this section. Anincoming beam 106 will then be totally internally reflected, asdescribed above, at the interface between the activated 98 andunactivated sections 100. This interface or boundary 102 can beestablished more definitely by having the second section 100, be of adifferent thickness than the first 98. This serves to direct theelectric field lines better so that less fringing is produced, and asharper interface boundary 102 is established.

[0069]FIG. 10 shows a perspective view of another system 11 formodulating or switching light beams which uses yet another version ofthe light modulating array 10 to perform channel separation. A singleprism-shaped protrusion 114 is shown, which can be electro-opticallyactivated by electrodes 116 to increase the index of refraction. Thiscauses the light beam to be bent towards the normal upon entry slightlydifferently than when the material is an inactive state. Thus when theelement is active, the light beam will follow a first path 118, and willemerge at a slightly different angle relative to the normal upon leavingthe element, thus following a first exiting path 120. In contrast, whenthe element is inactive, the light follows a second path 122 upon entry,and follows a second exiting path 124. Both of these second paths areshown in dashed line in FIG. 10. These first and second exiting paths120, 124 are separated by angle β, and they can be further directed bymirrored surfaces 126 to sensors 128 to produce separate channels. Theseparation of the paths and the separation angle has been exaggerated inthe FIG. 10.

[0070]FIG. 11 illustrates yet another version of the present lightmodulating array 10 in which end-mounted electrodes 130 each having anaperture 132 have been attached to the front faces 26 and rear faces 28of the protrusions 16. In this configuration, the electric field linesare collinear with the direction of incoming light beams 42. Theapplication of appropriate applied voltage results in the change inpolarized output in a manner similar to that discussed above. It is tobe understood that the above mentioned methods of splitting the outputinto separate channels, or using an external polarizer and sensor may beused, as well as mounting of elements on different substrate material,and variations in conductive pad placement.

[0071] It is also possible to have a light-producing element, such as adiode laser, with a modulating element physically attached at thelaser's output, in order to produce a single integrated element.

[0072] Another variation of the preferred embodiment uses sol-gelprocessing to create an array of elements that are fixed in a flexiblemedium. Sol-gel processing is a chemically based, relatively lowtemperature (400-800 degrees C.) method that can produce ceramics andglasses with better purity and homogeneity than higher temperature(2,000 degrees C.) conventional processes.

[0073] When using molding processes, two approaches are possible. In thefirst approach, a non electro-optic, optically transparent ornon-transparent matrix is prepared. Electrodes are deposited on the sidewalls. Then it is filled with soft, curable electro-optic material ofsol-gel type or polymer resin. It is then cured to produce an array ofelectro-optic modulators separated spatially by non electro-opticmaterial.

[0074] In the second approach, an electro-optically active matrix ofsolid or flexible material is prepared. Electrodes are deposited on theside walls. Then it is filled with soft, curable non electro-opticmaterial, of optically transparent or non transparent, sol gel type orpolymer resin. Then it is cured to produce an array of electro-opticmodulators separated spatially by non electro-optic material.

[0075] For the PLZT thin films made by the sol-gel process with 1-2 μmspacing between embedded adjacent electrodes, λ/2 voltages range from20-30 Volts for 0.5 μm thick films, to TTL levels (4-5 Volts) for 1-2 μmfilm thickness. This idea is very attractive for large area flat paneldisplay applications, which function like CRT tubes and which maysuccessfully compete with them. Because electrode spacing is necessarilyvery small to achieve low driving voltages, resulting pixel size is alsovery small, which makes this embodiment ideal for high-resolution flatpanel displays or spatial light modulators. This fine pixel structure isbelow typical resolution capability of the human eye, so for consumerapplications, sub-micron and micron size substructures may be aggregatedto produce standard sized pixels (usually dozens or hundreds ofmicrons). To simplify the manufacturing process and make it compatiblewith existing flat panel technology, the pixel size can be made larger.In this case, each pixel represents an interdigital pattern of PLZTembedded shutter electrodes.

[0076]FIG. 12 shows a top plan view of a modulator array 10 composed ofembedded electrodes 134 that are contained in a sol-gel matrix 136. Thearrow lines indicate electric field lines 138. The height of theelectrodes 134 (out of drawing plane) is defined by the thickness of thefilm. In the figure, light also travels perpendicular to the drawingplane. For non-polarized light, the modulator array 10 is placed inbetween two cross polarizers (not shown).

[0077] The electrode structures can be deposited either prior to thesol-gel film deposition, or after it, using standard etching ormicro-machining techniques. Using etching techniques and moldingprocesses, the height of the electrodes 134 can be much higher, 10 μm ormore with the same 1-2 μm spacing between electrodes. In this case,sol-gel can fill the spacings between electrodes 134 and the thin filmcan still be thin enough (a few microns) to guarantee the samefabrication process and similar process conditions. This will allowdriving or switching voltages on the TTL level (4-5 Volts) or below (1-3Volts and even lower). The arrays thus fabricated can be used in eithertransmissive or reflective modes. Additionally, the sol-gel material caneither be used to completely fill the gap between electrodes, or it caninstead be deposited on the sides of the electrodes as a coating. Ifused as a coating, an additional electrode can be added on the outerside of the sol-gel coating to make a complete element, each elementbeing separated from its neighbor by a gap or groove.

[0078] In addition to the above mentioned examples, various othermodifications and alterations of the inventive device 10 may be madewithout departing from the invention. Accordingly, the above disclosureis not to be considered as limiting and the appended claims are to beinterpreted as encompassing the true spirit and the entire scope of theinvention.

INDUSTRIAL APPLICABILITY

[0079] The present device 10 is well suited for application in a widerange of fields in which light modulators and high speed light switchingdevices are used, such as in high-speed printing, image processing andtelecommunications. The present invention 10 is also especially suitedfor use in flat panel displays and projection television.

[0080] Although the basic array structures 10 discussed above are in aone-dimensional line configuration, these may be configured and arrangedto form two-dimensional sheets of large size. Additionally, by use ofthe sol-gel process, they may be used to make a kind of thin flexibledisplay material almost like cloth, which may be used to cover threedimensional forms or perhaps even to make clothing.

[0081] The materials presently used in flat panel displays respond veryslowly to changes in display information. This leads to the commonlyobserved problem, especially in flat panel displays of laptop computers,that the display of a moving object will leave trails behind, due to thelag in the response of the display. The present invention, by contrast,is capable of switching speeds of 100 GHz and more, producing such fastresponse that it is beyond the ability of the human eye to registerindividual steps in a display of motion.

[0082] Prior art displays also may exhibit the problem of aliasing, orthe jagged edges sometimes seen around the outline of a displayed objectdue to the comparatively large size of pixels in a digital display. Bycontrast, the elements of the present invention 10 may be made assmaller than 1 μm×1 μm in cross section, each element being capable ofproducing an independent signal. Thus each element is potentially anindependent pixel. The use of the present invention completelyeliminates the problem of aliasing down to the microscopic scale.Indeed, the human eye cannot resolve such small elements. Thus for useon the scale of ordinary unaided human vision, the elements may begrouped into larger pixels, whose overall size can still be small enoughto provide far better image resolution than is presently available.There may also be applications in which microscopic pixel size isadvantageous, such as making microscopic photo masks for microchipmanufacture. The ungrouped pixels of the present invention are uniquelysuited for such uses.

[0083] The very small size of the elements allows low driving voltagesto be used to produce the necessary electric field density to induce thedesired electro-optic effect. TTL levels may be used with somematerials. The use of TTL level voltages has many significantadvantages. TTL level power supplies have been well developed over manyyears and are commonly available “off the shelf”. Thus power suppliescan be easily obtained for systems that utilize the present inventionwithout having to provide a customized power supply. This also allowseasier introduction of the present invention 10 into equipment that usesTTL devices and already has the appropriate power supply in place.

[0084] The present invention 10 also may be designed to utilize sub-TTLlevels. It is useful in many applications in which these smaller drivervoltages are supplied.

[0085] Prior art light modulators and optical switches that arefabricated on a common wafer without benefit of any feature to channelthe electric field lines commonly suffer from problems with cross-talkbetween the channels. This interferes with image clarity and can corrupttransmitted data. By contrast, by utilizing the discrete elements of thepresent invention 10, cross-talk between channels is practicallyeliminated, resulting in cleaner image production and improved accuracyand integrity of data transmission. This has very many industrialapplications in a wide variety of devices such as printers,telecommunications, and visual displays.

[0086] In addition, for telecommunications applications, prior art diodelasers which have been used, have typically suffered from the problem of“chirping” which is interference which can be produced when the voltagesupplied to a diode laser is rapidly modulated. In contrast, the presentinvention 10 modulates the optical output, rather than the diode laseritself. This greatly reduces interference and can eliminate the problemof chirping. This can be an important advantage for telecommunicationsapplications.

[0087] Another feature that makes the present invention 10 especiallydesirable for industrial applications is its ease of manufacture and lowcost. It can be made using existing technology by varying methods suchas micro-machining, laser ablation, selective etching in an electricfield, and molding by conventional means or using a sol-gel process. Formicro-machining, the same kinds of micro-saws as are presently used intrimming silicon wafers can be used to form the slots between theprojections.

[0088] Another method for manufacturing light modulating arrays 10 isthe use of sol-gel processing to create an array of elements that arefixed in a flexible medium. Sol-gel processing is a chemically based,relatively low temperature method that can produce ceramics and glasseswith better purity and homogeneity than higher temperature conventionalprocesses. Another of the attractive features of the sol-gel process isthe capability to produce compositions not possible with conventionalmethods.

[0089] Thin films of PLZT electro-optic ceramic made with the sol-gelprocess have a number of advantages relative to PLZT ceramics preparedfrom powders. Large surface areas of thin film can be created which havevery uniform (homogeneous) material structure. Small grain sizes areachievable, in the range of 10's of nm, with much less porosity comparedwith PLZT ceramics prepared from powders. A wide range of film thicknessfrom a few nanometers to a few microns can be produced.

[0090] Sol-gel manufacture also easily lends itself to high volumeproduction. It is inexpensive, suitable for large area spatial lightmodulators or flat panel displays and can utilize micro-machiningfabrication processes which are standard in the industry. It can be usedfor bright, ultra high-speed flat panel displays or spatial lightmodulators suitable for computer interconnects and high-speedtelecommunications with very wide viewing angles which may eventually beused to replace cathode ray tubes.

[0091] For the above, and other reasons, it is expected that the device10 of the present invention will have widespread industrialapplicability. Therefore, it is expected that the commercial utility ofthe present invention will be extensive and long lasting.

What is claimed is:
 1. A light modulating array comprising: a pluralityof discrete protrusions formed of electro-optic material, each discreteprotrusion being electrically and optically isolated from each other,said protrusions further having defined a top face, a bottom face, firstand second side faces, and front and back faces; and a plurality ofelectrodes associated with each of said protrusions, said electrodesbeing capable of inducing an electric field in said electro-opticmaterial for independently modulating one or more light beams which areincident upon one of said faces of said protrusions.
 2. The lightmodulating array of claim 1 wherein: said protrusions are formed from asingle wafer of electro-optic material and said bottom faces of saidprotrusions are integral with said wafer.
 3. The light modulating arrayof claim 1 wherein: said protrusions are formed on a separate substratelayer.
 4. The light modulating array of claim 1 wherein: saidprotrusions are separated by regions of dielectric material.
 5. Thelight modulating array of claim I wherein: each of said first side facesare angled such that incident light beams are internally reflectedwithin said protrusions.
 6. The light modulating array of claim 5wherein: said second side face is angled such that incident light beamsare directed to exit said protrusions.
 7. The light modulating array ofclaim 6 wherein: said first and second angled faces include a reflectivemeans.
 8. The light modulating array of claim I wherein: saidelectro-optic material is selected from the group consisting ofelectro-optic crystals, polycrystalline electro-optic ceramics,electro-optically active polymers, electro-optic semiconductors andelectro-optic glasses.
 9. The light modulating array of claim 8 wherein:said electro-optic material is PLZT where the lanthanum concentrationlies in the range of 8.5% to 9.0% of the overall composition.
 10. Thelight modulating array of claim 1 wherein: said electrodes are attachedto said first and second side faces of said protrusions.
 11. The lightmodulating array of claim I wherein: said electrodes are attached tosaid front and rear faces of said protrusions and said electrodesinclude an aperture for passage of light beams.
 12. The light modulatingarray of claim 2 wherein: said wafer includes a bottom surface; and anelectrode is attached to each top face of each of said protrusions andone or more electrodes contact said bottom surface of said wafer. 13.The light modulating array of claim 3 wherein: an electrode is attachedto each said top face of each said protrusion and said substrate layerincludes one or more electrodes which contact said bottom face of eachof the protrusions in the array.
 14. The light modulating array of claim1 wherein: each of said protrusions includes a first portion of saidelectro-optic material to which a plurality of electrodes is associated,and each of said protrusions further includes a second portion composedof material with an index of refraction matching that of said firstportion when no voltage is applied to electro-optically activate saidfirst portion, but said index of refraction of said second portion isless than the index of refraction of said first portion when said firstportion is electro-optically activated by application of appropriatevoltage; said first and second portions are in close conjunction witheach other such that a boundary is formed at the junction of said firstand second portions; and each of said protrusions is oriented withrespect to one or more light beams such that said each of the lightbeams enters each first portion of each protrusion and strikes saidboundary between said first and said second portions at an angle suchthat each light beam is totally reflected internally when said firstportion is electro-optically activated by application of sufficientvoltage, but which will pass unreflected through said boundary when saidfirst portion is not electro-optically activated.
 15. A light modulatingarray comprising: a plurality of discrete protrusions formed ofelectro-optic material, each discrete protrusion being electrically andoptically isolated from each other, said protrusions further beingformed in a prism shape having defined a top face, a bottom face, andfront and rear faces; a plurality of electrodes associated with each ofsaid protrusions, said electrodes being capable of inducing an electricfield in said electro-optic material for independently modulating one ormore incident light beams; and each of said prism shaped protrusions isoriented with respect to one or more light beams such that each lightbeam incident upon said front face of said protrusion enters eachprotrusion traveling a first path and emerging at a first angle fromsaid rear face of said protrusion when no voltage is applied toelectro-optically activate said protrusion, but each light beam travelsa second path and emerges at a second angle from said rear face of saidprotrusion when said protrusion is electro-optically activated byapplication of appropriate voltage.
 16. A light modulating arraycomprising: a matrix of electro-optic material; and said matrixcontaining a plurality of embedded adjacent electrodes, said electrodesbeing capable of inducing an electric field in said electro-opticmaterial for independently modulating one or more light beams which areincident upon said matrix of electro-optic material.
 17. A lightmodulating array as in claim 16 wherein: said electrodes are embedded insaid matrix material by a process selected from the group consisting ofsol-gel deposition, molding, etching of the matrix followed by electrodeplacement, and micro-machining of the matrix.
 18. A system formodulating light comprising: one or more discrete protrusions formed ofelectro-optic material, each discrete protrusion being electrically andoptically isolated from each other, said protrusions having defined atop face, a bottom face, one or more side faces, and front and backfaces; a plurality of electrodes associated with each of saidprotrusions, said electrodes being capable of inducing an electric fieldin said electro-optic material for independently modulating one or morelight beams incident upon one of said faces of said protrusions, thelight beams being linearly polarized in a first polarizationorientation; a power supply capable of supplying sufficient voltage toinduce a desired polarization shift from a first polarizationorientation to a second polarization orientation in a beam of polarizedlight entering said protrusions; conductive means for conductingelectricity from said power supply to said plurality of electrodes;switching means for controlling application of voltage to saidelectrodes through said conducting means; and separation means forseparating light of a first polarization orientation from light of asecond polarization orientation.
 19. The system for modulating light ofclaim 18 wherein: said conductive means includes conductive pads whichare connected to said electrodes in a configuration to be selected fromthe group consisting of two conductive pads on the top surface of eachprotrusion, a conductive pad on each side surface of each protrusion,and a conductive pad on the top surface of each protrusion and aconductive pad on each of one or more electrodes which are associatedwith the bottom of each protrusion,
 20. The system for modulating lightof claim 18 wherein: said separation means is an output polarizer havinga polarization orientation, said polarizer being positioned to transmitlinearly polarized light output from said protrusions having the samepolarization orientation as that of said output polarizer.
 21. Thesystem for modulating light of claim 18 wherein: said separation meansis a beam splitter, said beam splitter being positioned so that light ofa first polarization orientation is passed through said beam splitter,and light of a second polarization orientation is reflected.